In vivo Evaluation of 11ß-Hydroxysteroid Dehydrogenase Activity in the Rabbit Eye

Abstract

Purpose:: Steroids are used in a diverse range of conditions in clinical ophthalmology and one of the most significant complications is corticosteroid-induced glaucoma, which is characterized by an increase in intraocular pressure (IOP). 11ß-hydroxysteroid dehydrogenase-1 (11ß-HSD1) is known to catalyze the interconversion of hormonally inactive cortisone to hormonally active cortisol. Carbenoxolone (CBX), an11ß-HSD1 inhibitor, has been shown to reduce IOP in healthy volunteers. The purpose of this study was to: 1) develop an in vivo model for the assessment of cortisone to cortisol conversion in the eye and; 2) assess the PK/PD relationship of topical treatment with 11ß-HSD1 inhibitors.

Methods:: Potent and selective 11ß-HSD1 inhibitors were topically administered to the rabbit eye. Two hours prior to the tissue harvest time point, cortisone was injected into the subconjunctival space in the same eye. Tissues were then evaluated for cortisone, cortisol and compound levels by LC/MS/MS. Cortisol activity was determined using a secondary mechanistic pLuc-GRE assay.

Results:: The model is useful in determining the effects of topically dosed 11ß-HSD1 inhibitors on the conversion of cortisone to cortisol in the eye. Topical treatment with 11ß-HSD1 inhibitors resulted in complete inhibition of cortisone conversion to cortisol. The reduction of cortisone conversion was time- and dose-dependent as well as dependent on dosing volume (suggestive of increased spillover and washout with greater dosing volume). Contralateral effects were also noted suggesting that the inhibitor was getting to the contralateral eye by an unknown route. Changes in cortisol levels following treatment also resulted in a reduction of steroid-induced GR transcriptional activity of aqueous humor samples as assessed via pLuc-GRE assay.

Conclusions:: The rabbit model is useful for the assessment of inhibition of cortisone to cortisol conversion by 11ß-HSD1 inhibitors in the eye. Topical delivery of 11ß-HSD1 inhibitors can reduce or inhibit the conversion of cortisone to cortisol. This finding coupled with the fact that CBX has been shown to reduce intraocular pressure in healthy volunteers would suggest that steroid control with 11b-HSD1 inhibitors may play a role in IOP control and could be useful in the therapeutic management of glaucoma.

Keywords: ACAID